<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>

    </style>
</head>
<body>

</body>
<script>
    /*aaa("-")
    function  aaa(b){
        var c=1  2
    }*/
    var a=10;
    var b="+";
    var c=20;
    fn(a,b,c)
    function fn(a,b,c) {
        var d=a+b+c;
        alert(d)
        alert(eval(d))
    }
</script>
</html>